Cross-linking process of polyvinyl chloride



United States Patent 3,310,522 CROSS-LINKING PROCESS OF POLYVINYLCHLORIDE Sakae Takahashi, Kanagawa-ku, Yokohama, Hiroshi Nishimura,Kohoku-ku, Yokohama, and Mitsuo Inui, Nishi-ku, Yokohama, Japan,assignors to The Furukawa Electric Company Limited, Tokyo, Japan, acorporation of Japan No Drawing. Filed July 16, 1962, Ser. No. 210,180

- Claims priority, application Japan, July 19, 1961,

36/25,979 3 Claims. (Cl. 260-41) being linear polymers, they easilydissolve in an organic solvent.

As the method for obviating such defects, it has been known thatirradiation is applied to polymer or copolymers of vinyl chloride toeffect cross-linking, but the irradiation needs a special apparatuswhich is very inconvenient for handling, so that its practical use isdifiicult, and, accordingly, there is no known process adapted forcommercial purposes.

In carrying out the invention a mixture which contains (1) 100 parts byweight of polyvinyl chloride or copolymer of vinyl chloride-vinyl alkylether, or of vinyl chloride-vinyl esters of aliphatic acid, e.g'., vinylchloridevinyl acetate or vinyl chloride-vinyl stearate; (2) a requisitequantity of plas-ticizer, such as dioctyl phthalate; (3) a requisitequantity of a stabilizer, such as basic lead carbonate; (4) at least 5parts by weight, preferably to parts by weight of metal oxide or metaloxides, such as zinc, lead, magnesium, antimony, calcium, iron, cadmiumand barium and (5) 0.5 to 5.0 parts by weight of a member of a classconsisting of Z-mercapto-imidazoline, Z-mercapto-thiazoline ordi-orthotolyl guanidine salt of dicatechol borate is heated to atemperature of above 130 C. to cause cross-linking between molecules ofpolymer or copolymers of vinyl chloride, thereby causing the said resinto be converted into a three dimensional structure with increased heatresistance, reduced deformation, :insolubility in organic solvent, andimproved mechanical properties.

The heating time has intimate relation with the he-ating temperature andas the temperature is raised higher the heating time can be shortened.

The plasticizers and stabilizers contained in the above mixture includethose which areusually applicable to poly- 1 vinyl chloride resin orcopolymerized resin thereof.

It is yet impossible exactly to explain the mechanism of cross-linkingin accordance with the invention, but it may be considered that byheating a mixture of polymer or copolymers. of vinyl chloride and metaloxide there occurs dehydrochlorination of molecules of polymer or3,310,522 Patented Mar. 21, 1967 copolymers of vinyl chloride in saidmixture, thereby resulting in cross-linking between molecules.

The reason why the mixture ratio of the metal oxide is defined at 5 ormore parts by weight is that below 5 parts by weight the cross-linkingeffect is weak.

Any of the above metal oxides may be used alone or in combination of 2or more without objection.

The reason why the vulcanizing accelerator such as 2-merca-pto-imidazoline is added according to the invention is toaccelerate the cross-linking effect of polymer or copolymers of vinylchloride as shown in Table I.

Further, according to the invention, fillers such as carbon black,calcium carbonate, clay, talc, silica and diatomaceous earth may beadded Without objection, and by adding a substantially large quantitythe cost of the resinous mixture of polymer or copolymers of vinylchloride can be lowered. When a large quantity of the above filler isadded to the conventional polyvinyl chloride resinous mixture, theresulting mixture becomes brittle and causes a condition which is notsuitable for use. On the contrary, in accordance with the invention, asmuch as or more parts by weight of the filler to 100 parts by weight ofthe resin in the mixture of polymer or copolymers of vinyl chloride maybe added without becoming brittle.

The invention will 'be explained with examples, wherein part meansweight part.

Example 1 Basic composition: Parts Polyvinyl chloride resin (trade nameGeon 101 EP) 100 Dioctyl phthalate 60 Basic lead carbonate 10 Calciumcarbonate 10 To the above basic composition were added 12 parts of zincoxide, 6 parts of antimony oxide and 3.6 parts ofZ-mercapto-imidazoline, and the mixture was heated at C. for 30 minutesto effect cross-linking.

Examples 2 and 3 To a mixture of said basic composition shown in Example1 were added 18 parts and 27 parts respectively of Zinc oxide, and 3.6parts of Z-mercapto-imidazoline, and heated at 160 C. for 30 minutes.

Example 4 To said basic composition were added 27.0 parts of magnesiumoxide and 3.6 parts of Z-mercaptodmidazoline, and heated at 160 C. for30 minutes.

Example 5 TABLE 1 Conven- Example Example Example Example Example tional(1) 2) (3) (4) product Tensile strength, kg./n1m. 1. 70 2. 26 2.10 2.142.11 2. 24 Elongation (percent) 300 350 360 350 290 360 Swelling(percent) Dissolved 280 510 410 290 250 NOTE: Swelling ratio is a ratioof weight measured before and after dipping into methyl ethyl ketone at70 C. for 5 hours.

.1 TABLE 4 Furthermore, heat deformation percent (deformation 2 after aload of 4 kg/cm. 1s oontlnuously applied for Example (8) Conventionalminutes at the measuring temperature shown in Table 2) compound andrecovery percent (recovery 10 minutes after the load is removed afterthe measurement of deformation) of the giznsiletstrerggth (kgo/mmfl) 2 22 1. 23

onga 1011 pereen V cross-linked product under Example 1 and also of con20 Swelling mic (percent) 230 Dissolved ventional product are shown inTable 2.

TABLE 2 Conventional compound Example (1) Measuring temperature, C.Deformation, Recovery, Deformation, Recovery,

percent percent percent percent 14. e 98. r 12. 9 99. 5 24. s 95. 1 14.7 9s. 0 33. 6 95. 1 23. 4 97. 8 78. 6 32. 2 34. 9 92. 0

Example 6 As apparent from the above table, the mechanical .prop- Partsertie and solvent resistance .of polymer or copolymers of Copolymerofvinyl chloride-vinyl isobutyl ether 100 vinyl chloride can beconsiderably improved by simple Dioctylphthalate 4 process according tothe invention without special ap- Tribasic lead sulphate 7 paratus andit ShOWs that these resins had been cross-linked Basic l slllphite 5apparently and had excellent eff t,

To the above basic composition were added 13 parts of antimony oxide, 10parts of zinc oxide and 3 parts of 2- mercapto-imidazoline, and themixture was heated 160 C. for 30 minutes for vulcanization. The resultsof measuring the mechanical properties and solvent resistance are shownin Table 3.

The similar test was effected of a conventional mixture of the abovebasic composition only.

To the above basic composition were added 10 parts of antimony oxide, 20parts of zinc oxide, 4 parts of 2- mercapto-imidazoline, and parts ofthermal black, and the mixture was heated at 160 C. for 30 minutes toefiect vulcanization.

The same test was effected of the conventional mixture of the abovebasic composition only.

What We claim is:

1. In a process for cross-linking polyvinyl chloride the improvementwhich comprises adding to a polymer selected from the group consistingof homopolymer and copolymers of vinyl chloride, a mixture consistingessentially of between about 10 to 40 parts by weight of at least onemetal oxide selected from the group consisting of Zinc, lead, antimony,calcium, iron, cadmium, barium and magnesium oxides and 0.5 to 5.0 partsby weight of 2-mercapto-imidazoline, both based on parts by weight ofsaid member, and vulcanizing said mixture at a temperature above C. 'forat least approximately 30 minutes in order to complete thevulcanization.

21A process according to claim 1, further comprising adding to themixture before vulcanization about 5 to parts by weight of a fillerselected from the group consisting of carbon black, calcium carbonate,clay, talc, silica and diatomaceous earth.

3. A process according to claim 1, wherein said mixture contains a vinylchloride copolymer selected from the group consisting of vinylchloride-vinyl alkyl ether and vinyl chloride-vinyl aliphatic estercopolymer.

References Cited by the Examiner UNITED STATES PATENTS 2,157,997 5/1939Brous 26092.8 2,274,616 2/1942 Raynolds 26086 (Other references onfollowing page) 5 6 UNITED STATES PATENTS New York, Reinhold PublishingCo. (chapters 7-8 relied $419,166 /1947 R t 1. 2 25447; 3,017,379ll/196,2 F2558 e a 260- 4 Forman, D. B., at 211.: Vulcanization ofNeoprene Type 1 3 07 Nimoy et 1 26O 41 W, Ind. & Eng. Chem. 42, 686-91p. 691.

- 5 MORRIS LIEBMAN, Primary Examiner. OTHER REFERENCES K. B. CLARKE, A.HOLTZ, J. FROME,

Alliger, G., et al.: vulcanization of Elastomers, 1964, AssistantExaminers.

1. IN A PROCESS FOR CROSS-LINKING POLYVINYL CHLORIDE THE IMPROVEMENTWHICH COMPRISES ADDING TO A POLYMER SELECTED FROM THE GROUP CONSISTINGOF HOMOPOLYMER AND COPOLYMERS OF VINYL CHLORIDE, A MIXTURE CONSISTINGESSENTIALLY OF BETWEEN ABOUT 10 TO 40 PARTS BY WEIGHT OF AT LEAST ONEMETAL OXIDE SELECTED FROM THE GROUP CONSISTING OF ZINC, LEAD, ANTIMONY,CALCIUM, IRON, CADMIUM, BARIUM AND MAGNESIUM OXIDES AND 0.5 TO 5.0 PARTSBY WEIGHT OF 2-MERCAPTO-IMIDAZOLINE, BOTH BASED ON 100 PARTS BY WEIGHTOF SAID MEMBER, AND VULCANZING SAID MIXTURE AT A TEMPERATURE ABOVE130*C. FOR AT LEAST APPROXIMATELY 30 MINUTES IN ORDER TO COMPLETE THEVULCANIZATION.